The BICEP2 Collaboration used a telescope at the South Pole to detect the signal in the oldest light it is possible to observe. At the time of the group's announcement in March, the discovery was hailed as a near-certain Nobel Prize. But the criticism since has been sharp. Rival groups have picked holes in the team's methods and analysis.
On Thursday, the BICEP2 collaboration formally published its research in a peer reviewed journal - Physical Review Letters (PRL). In the paper, the US-led group stands by its work but accepts some big questions remain outstanding. And addressing a public lecture in London, one of BICEP2's principal investigators acknowledged that circumstances had changed. "Has my confidence gone down? Yes," Prof Clem Pryke, from the University of Minnesota, told his audience.